Compact discs have become a standard medium for recording of audio and video information in digital format. The replication of compact discs involves molding of a raw disc, sputtering a metallic coating on the raw disc to form a metallized disc and applying a lacquer coating to the metallized , disc. The raw disc is molded plastic having data pits which contain digital information. The metallic coating forms a reflective layer that allows a scanning laser beam to read the digital information from the compact disc (CD). The lacquer coating functions as a protective layer for the metallic coating and provides a smooth surface for printing.
The steps in the replication of compact discs are typically automated to the extent that is practical. The throughput in terms of compact discs processed per unit time is an important parameter in achieving efficient and low cost production. Thus, it is critical to design the processing equipment so that the processing time and the handling time (the time required to move discs into and out of processing stations) are as short as possible.
The coating process, known as spin coating, involves dispensing a quantity of lacquer onto the compact disc surface, spinning the disc at high speed to produce a thin coating of lacquer on the metallized disc, and curing the lacquer coating with ultraviolet radiation. Two basic types of spin coating systems are known. In a first system, known as a one bowl spincoater, the lacquer is dispensed onto the disc surface and the disc is spun at high speed to distribute the lacquer over the disc surface in a single process station, or bowl. This system is relatively simple, compact and low in cost. However, the one bowl spincoater has a relatively long process time because dispensing of lacquer and spinning are performed serially.
In a two bowl spincoater, lacquer is dispensed onto the disc surface in a first process station, or bowl, and disc spinning to distribute the lacquer is performed in a second process station, or bowl. A system of this type is disclosed in U.S. Pat. No. 5,069,155, issued Dec. 3, 1991 to Kunze-Concewitz et al. An advantage of the two bowl spincoater is that productivity is increased because dispensing of lacquer and spinning are performed simultaneously at different stations. However, the time required for transfer of the compact disc from the first station to the second station adds to the total process time and reduces throughput. Furthermore, the two bowl spincoater is more complicated, is larger and has higher cost than the one bowl spincoater.
U.S. Pat. No. 4,320,914, issued Mar. 23, 1982 to Simon, relates to a clamping-type holder for clamping test tubes. Balls are positioned in openings in a cylinder so that when a housing cylinder moves downward, the balls move radially to engage the test tube.
U.S. Pat. No. 4,071,149, issued Jan. 31, 1978 to Deguchi, discloses an apparatus for piling apertured articles in stacks for storage. A control member is installed at the lower end of a pipe member so that projectable members project outwardly through openings due to the frustoconical surface of the control member, thereby grasping an object.
All of the known prior art compact disc coating systems have one or more disadvantages, including relatively low throughput, complex construction and relatively high cost. It is desirable to provide methods and apparatus for coating compact discs that overcome one or more of these disadvantages.